Volcano Watch

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

June 21, 2012

Tarawera's 1886 eruption is one to remember

View from near the top of Mount Tarawera looking northeast along part of the string of explosion craters that split the volcano on June 10, 1886. Mount Edgecumbe stands in the distance.

Hawaiʻi's eruptions over the past several decades have been relatively benign, being characterized mostly by persistent lava lake activity or lava flows and occasional episodes of lava fountaining. Even the recent explosive events at Halemaʻumaʻu, which have happened sporadically over the past 4 years, were very small and impacted only a tiny area of the summit. With such activity seeming to be the norm here, we tend to forget that basaltic volcanism can sometimes be much more violent.

June 10, just a few weeks ago, marked the anniversary of the deadly 1886 eruption of Tarawera volcano, on New Zealand's North Island. Having last erupted in the 14th century, Maori and European settlers did not know that Mount Tarawera was an active volcano. Small towns and villages dotted the surrounding landscape, and tourists visited hot springs at nearby geothermal areas.

Shortly after midnight on June 10, people in those villages and towns were shaken awake by a swarm of violent earthquakes, which were felt throughout the North Island. Those living close to the volcano soon found themselves in a struggle for survival. A basaltic dike, with a lava composition similar to that erupted in Hawaiʻi, was forcing its way to the surface, breaking the ground above. At about 2:00 AM, the night sky was suddenly lit by an eerie glow as incandescent columns of tephra began to erupt from the fissure that was splitting Tarawera down the middle. Clouds of ash, with lightning flashing inside, reached to a height of 10 km (6 mi).

The dike continued to extend, eventually reaching a length of 17 km (11 mi), with new blast craters opening sequentially. Near its southeastern end the fissure intersected the Rotomahana geothermal field and triggered a series of powerful phreatomagmatic explosionsones caused by the interaction of magma and waterthat destroyed the Pink and White Terraces, a geothermal feature considered one of the wonders of the world. The rumbling of the eruption was audible at the northern tip of the South Island, 420 km (260 mi) away.

The surrounding landscape was quickly blanketed by a thick layer of muddy ash, stripping away vegetation and causing roofs to collapse on many who had sought refuge indoors. By the time the eruption ended at about 6:00 AM, five Maori villages had been buried or destroyed, accounting for most of the 108 people estimated to have died. This devastating event shook the foundations of the local Maori people, who placed a taboo on the mountain that forbid Maori visitation to this sacred site for 100 years.

The 1886 eruption of Mount Tarawera is a long way off, in both time and distance, but could something like that happen here in Hawaiʻi? The answer is, "sort of." While a fissure eruption of the intensity of that at Tarawera is not likely at Kīlauea, our volcano has hosted extremely powerful explosive eruptions from its summit.

Descriptions of these events have been highlighted in past Volcano Watch articles, and their occurrence is evident in the thick tephra layers studded with ballistic blocks that surround Kīlauea's caldera. An eruption like that, though different in style, could be equally as devastating as that at Mount Tarawera if it were to happen today at Kīlauea. There is little need to worry though. Large explosive basaltic eruptions, like those in Kīlauea'sand Tarawera'spast, are rare indeed.

Kīlauea Activity Update

A lava lake within the Halemaʻumaʻu Overlook vent resulted in night-time glow that was visible from the Jaggar Museum overlook during the past week. The lake has been about 6080 m (200260 ft) below the floor of Halemaʻumaʻu Crater and visible by HVO's Webcam through much of the last month. This past week the level fluctuated slightly due to several deflation-inflation (DI) cycles at the summit.

On Kīlauea's east rift zone, surface lava flows on the pali and coastal plain continued advancing towards the ocean. As of Wednesday, June 20, the flows were about 800 m (0.5 miles) from the ocean; there was no active ocean entry. Within Puʻu ʻŌʻō crater, a lava pond was active and several small lava flows were erupted onto the crater floor over the past week.

Three earthquakes were reported felt across the island of Hawaiʻi during the past week. A magnitude-3.0 earthquake occurred at 2:31 p.m., HST, on June 14, 2012, and was located 13 km (8 mi) southeast of Waimea at a depth of 15 km (9 mi). A magnitude-3.8 earthquake occurred at 2:18 p.m., on June 15 and was located 14 mi (23 km) southwest of Waikōloa Village at a depth of 40 km (25 mi). A magnitude-2.9 earthquake occurred at 1:01 p.m., HST, on June 19 and was located 4 km (2 mi) southeast of Kīlauea summit at a depth of 4 km (2 mi).